Page 1/12

A new anatomic zone division within the cervicalspinal canalYadong Liu 

Capital Medical UniversityLi Liu 

Capital Medical UniversityChao Kong 

Capital Medical UniversityXueming Chen  ( xuemingchen@sina.com )Xin Yuan 

Capital Medical UniversityYan Gao 

Capital Medical UniversityYun Guan 

Johns Hopkins University

Research article

Keywords: cervical spondylosis; ventral nerve rootlets; morphology; anatomic zone

Posted Date: January 17th, 2020

DOI: https://doi.org/10.21203/rs.2.21245/v1

License: This work is licensed under a Creative Commons Attribution 4.0 International License.  Read Full License

Page 2/12

AbstractBackground: Detailed anatomical information is important for identifying the origin and anatomic basisof symptoms in cervical spondylosis patients, but very little quantitative data have been reported. Thisstudy characterized the morphologic features of cervical spinal nerve rootlets and de�ned different zonesat cervical spinal canal to provide an anatomic basis for studying cervical spondylosis. Methods: Tencervical spines from C2 to T1 were obtained for the present study. We de�ned three zones from midline tolateral part (zone I, II and III) and two zones from cranial to caudal (zone P and zone IP) on the coronalplane within the cervical spinal canal. Quantitative anatomy of the zones at different cervical segmentswere measured including: 1) horizontal widths of zone I, II and III; 2) Length of the cervical spinal cordsegment at the ventral rootlets (LV); 3) The pedicle height (PH, zone P) and the inter-pedicle height (IPH,zone IP); 4) The distance between the superior margin of pedicle and the exit of the uppermost ventralnerve rootlet (PN).  Results: There was a trend that the horizontal widths of zone I gradually decreasefrom C4 to C8 but without signi�cant differences (P=0.98). The value of zone II at C4 was signi�cantlyless than that at other levels (P=0.008). The value of zone III increases from C4 to C8, and the values atC7 and C8 were signi�cantly higher than those at C4, C5 and C6 (P=0.032). PHs and IPHs were notsigni�cantly different between different levels (P1=0.365; P2=0.240). The values of LV at C4 and C8 weresmaller than those of C5, C6 and C7 (P=0.001). The value of PN showed an increasing trend. At C4, theuppermost ventral rootlet was at about the same height as C3 pedicle, while C8 uppermost ventral rootletwas at the same level as the inferior part of C6 pedicle. Ventral intradural intersegmental connectionswere found in three intersegments (two specimens) out of 20 intersegments (15%). Conclusions: Thecurrent de�nition of anatomic zones may be useful for an accurate diagnosis of cervical spondylosis anda safe and effective anterior decompression surgery.

BackgroundCervical spondylosis is often caused by degenerative disc disease which may lead to neck pain,radiculopathy, and myelopathy [1-3]. Theoretically, cervical radiculopathy is due to compression of thenerve roots, whereas cervical myelopathy is resulted from compression of the spinal cord. Radiculopathyand myelopathy patients often have distinct syndromes [4], and hence the pathogenesis diagnosis can berelative easily achieved. Comparatively, it is more challenging to correctly diagnose myeloradiculopathy,as patients may show complicate syndromes, including signs of nerve root dysfunction in the upperlimbs and symptoms of long tract compression affecting the lower limbs.

The pathogenic mechanisms of myeloradiculopathy remain unclear, and it has been di�cult to ascertainwhether the dysfunctions are due to compression of the nerve root and/or the spinal cord [5]. In particular,patients with cervical radiculopathy may have various symptoms without clear nerve root location.Anatomic differences in brachial plexus may partially underlie the large variation of clinical symptoms ofcervical radiculopathy patients [6]. Since adjacent dorsal rootlets may have intradural intersegmentalconnections, compression of one dorsal rootlet can lead to impairments at adjacent rootlets leading tomore symptoms. A previous study showed an increased obliquity of nerve roots, especially in the lower

Page 3/12

cervical region, when these roots pass downward before reaching intervertebral foramina [8]. Accordingly,it has been di�cult to ascertain whether the nerve roots are compressed above or at the correspondingdisc level in imaging study.  

Detailed anatomical information of the cervical spinal cord and nerve roots is important for identifyingthe origin and anatomic basis of symptoms in cervical spondylosis patients, which is essential to usesurgical intervention to decompress the affected neural structures and avoid complications. By dissectingcervical spinal cord of adult cadavers, we characterized the morphologic features of cervical spinal nerverootlets and de�ned different zones at cervical spinal canal. Current �ndings provide an anatomic basisfor future study to differentiate subtypes of cervical spondylosis and examine the underlyingmechanisms.

MethodsCervical spines were harvested from 10 formalin-�xed adult cadavers (6 males, 4 females, aged 67 ± 12.1years) without cervical metastasis or gross deformities as scoliosis or kyphosis. These cadavers wereobtained from the Department of Human Anatomy, Capital Medical University, China. The researchprotocol for this study was approved by Institutional Review Board at LuHe Hospital, Capital MedicalUniversity.

Cadaveric dissections

The cervical spines were �xed in supine position. Soft tissues super�cial to vertebrae were removed. Thevertebral bodies and the anterior tubercle of transverse process from C3 to C7 were resected completely.The posterior longitudinal ligament from the anterior dura was then resected with caution. The dura andarachnoid membrane were excised carefully from C4 to C8 without damaging the spinal cord and ventralnerve rootlets. The anterior part of nerve root sleeves was also resected to provide a unobstructedobservation of the ventral nerve rootlets (Figure 1).

Anatomic zones in the coronal plane

In the coronal plane, the anterior surface of spinal canal was divided into three zones from midline tolateral part: zone I (medial zone), zone II (paramedian zone), and zone III (lateral zone) (Figure 2). Zone Irepresents the area between bilateral origins of ventral nerve rootlet. Zone II contains the area betweenthe origin of ventral nerve rootlets and lateral border of spinal cord. Zone III represents the area betweenlateral border of spinal cord and medial margin of the pedicle. Two

zones were de�ned from cranial to caudal: pedicle zone (zone P) and interpedicle zone (zone IP). Zone Pde�nes the area between the upper and lower margins of the corresponding pedicle, which contains themajor part of corresponding spinal cord segment and ventral nerve rootlets. Zone IP includes the areabetween the lower margin of the upper pedicle and the upper margin of the lower pedicle, which contains

Page 4/12

the caudal part of corresponding spinal cord segment and ventral nerve rootlets as well as the cranialpart of inferior segmental spinal cord and the ventral nerve rootlets (Figure 2).

Parameters

The measurements of the anatomic structures from C4 to C8 include: 1) Horizontal widths of zone I, IIand III (Figure 2); 2) Length of the cervical spinal cord segment at the ventral rootlets (LV, Figure 2); 3) Thepedicle height (PH, zone P) and the interpedicle height (IPH, Figure 2, zone IP); 4) The distance betweenthe superior margin of pedicle and the exit of the uppermost ventral nerve rootlet (PN, Figure 2).  Allmeasurements were performed bilaterally and the mean values were reported. The widths of zone I, II, andIII were measured at three different levels (uppermost, middle, lowermost) and the mean values were usedfor comparison. The linear measurements were obtained using a digital caliper. All parameters weremeasured twice by two researchers.

Statistical analysis

The differences between parameters measured at different levels were compared by one-way analysis ofvariance (ANOVA) with LSD (least signi�cant difference) post-hoc test. All statistical analyses wereconducted with using SPSS 21.0. Data are presented as mean ± standard deviation (SD), and thestatistical signi�cance was viewed as P<0.05.

ResultsHorizontal widths of zone I, II and III

There was a trend that the horizontal widths of zone I gradually decrease from C4 to C8 (Table 1).However, the horizontal widths of zone I were not signi�cantly different between different levels (F=2.157,P=0.98). The value of zone II at C4 was signi�cantly less than that at other levels (F=4.228, P=0.008). Thevalue of zone III increases from C4 to C8, and the values at C7 and C8 were signi�cantly higher thanthose at C4, C5 and C6 (F=3.050, P=0.032). The example of zone division and the contained neuralstructures were illustrated in Figure 3. After removing the vertebral body and intervertebral disc,compressions at zone I and zone II were identi�ed in two samples (Figure 4).

 Table 1. The horizontal widths of zone I, II and III from C4 to C8 (mm)  C4 C5 C6 C7 C8zone I 6.11±0.63 5.58±0.49 5.69±0.59 5.45±0.62 5.11±0.62zone II 2.35±0.61** 3.34±0.56 3.56±0.68 3.73±0.61 3.51±0.69

zone III 4.22±0.57 4.49±0.68 4.98±0.68 5.01±0.82* 5.21±0.76*

Note: Zone I: There was no significant difference in horizontal width between different levels.Zone II: * * p<0.01 versus C 5,6,7,8. Zone III: * p<0.05 versus C 4, 5,6.

Page 5/12

Longitudinal heights of zone P and zone IP

The pedicle height (PH) and the interpedicle height (IPH) were measured to represent the longitudinalheights of zone P and zone IP (Table 2). PHs and IPHs were not signi�cantly different between differentlevels (F1=1.121, P1=0.365; F2=1.458, P2=0.240).

         Table 2. The pedicle height (PH) and the interpedicle height (IPH) from C3 to C7 (mm)  C3(C3/4) C4(C4/5) C5(C5/6) C6(C6/7) C7(C7/T1)PH 7.9±0.88 8.52±1.1 8.18±1.26 8.53±1.29 9.12±1.16IPH 8.15±1.09 8.29±0.94 7.85±1.88 7.23±0.46 7.17±0.77

Note: C3(C3/4) means PH of C3 and IPH of C3/4. PH, pedicle height; IPH, interpedicle height. 

Longitudinal length of the cervical spinal cord segment at ventral rootlets

The mean value of LV from C4 to C8 was 10.92±1.95, 14.64±2.33, 13.27±1.33, 12.30±1.48, and10.28±2.09 mm respectively. The values of LV at C4 and C8 were smaller than those of C5, C6 and C7(F=6.177, P=0.001).

Anatomic relation between the segmental ventral rootlets and pedicle

The distance between the superior margin of pedicle and the uppermost ventral rootlet (PN) wasmeasured to re�ect the relative position of segmental ventral rootlets and pedicle. From C3 to C7 pediclelevel, the value of PN was 0.33±0.87, 3.86±2.23, 4.11±2.36, 3.94±2.18, and 5.19±2.09 mm 7 (F=5.809,P=0.001). At C4, the uppermost ventral rootlet was at about the same height as C3 pedicle, while C8uppermost ventral rootlet was at the same level as the inferior part of C6 pedicle, which explains whysome patients with compression at C6/7 have symptoms of C8.

Ventral intradural intersegmental connections

Ventral intradural intersegmental connections were found in three intersegments (two specimens) out of20 intersegments (15%). One specimen had bilateral connections while the other had unilateralconnections (Figure 5).  Both connections were found in C5/6 segment between C5 and C6 ventralrootlets.

DiscussionCervical spondylosis encompasses different symptoms including both motor and sensory abnormalitiesas radiculopathy, myelopathy and myeloradiculopathy. However, the radiological �ndings in manypatients do not match well with their symptoms [5]. A better understanding of the anatomic basis ofcervical spondylosis may help to �nd the reasons for this mismatch. Veleanu et al. [9] initially divided the

Page 6/12

nerve groove into two portions: radicular portion and portion of the anterior ramus of the transverseprocess, but did not provide quantitative data. Ebraheim et al. [10] described the cervical nerve grooveaccording to the different anatomic features along its length, and divided the nerve groove into threezones: medial (pedicle), middle (vertebral artery), and lateral. The medial zone was suggested to play animportant role in the etiology of cervical spondylotic radiculopathy [8]. However, this zone division wasfocused on the cervical nerve groove, but did not include the spinal cord and ventral nerve rootlets withinthe spinal canal.

To better understand the etiology of cervical spondylosis which is important to accurate diagnosis fordecompression site, we de�ned three zones from midline to lateral part and two zones from cranial tocaudal on the coronal plane. The three zones from midline to lateral part were: zone I (medial zone), zoneII (paramedian zone), and zone III (lateral zone). The coronal widths of zone I were not signi�cantlydifferent between C4-C8 levels. Since zone I contains only spinal cord and anterior spinal artery, localizedcompression in zone I may cause myelopathy without radiculopathy. Zone II contains cervical ventralnerve rootlet origin and lateral border of spinal cord. Compression in zone II may cause both myelopathyand radiculopathy. Ebraheim et al. [10] illustrated the importance of nerve root groove, but notpreforaminal area, in the etiology of cervical spondylotic radiculopathy. Osteophytes of the posterolateralcorner of the vertebral body, uncinated process, facet joints and lateral intervertebral disc herniation areoften observed in zone III [11]. In the preforaminal area, compression in zone III can be missed by clinicalexamination, leading to misdiagnosis and inadequate decompression.

Cervical spondylotic amyotrophy (CSA) is characterized by weakness and wasting of upper limb muscleswithout sensory or lower limb involvement [12-14]. The underlying mechanisms of CSA may involvedamages to the ventral nerve rootlets, and vascular insu�ciency to the anterior horn cells. The de�nitionof different zones is important for the diagnosis of CSA. Compression of zone I may cause anterior spinalartery impingement leading to dysfunction of anterior horn cells, which may partially explain why amoderate compression of the central canal sometimes led to CSA [13]. The compression at zone II willimpair the ventral nerve rootlets and anterior horn of spinal cord, which may cause motion dysfunctionwithout sensation loss (Figure 6). The compression at zone III de�ned in current study may only impairthe ventral nerve rootlets. Since zone III at C6/7 contains ventral nerve rootlets of C7 and C8, compressionin this region may cause CSA at both levels (Figure 3). Thus, the de�nition of zone division is particularlyimportant to correct diagnosis of CSA and decompression of the ventral nerve rootlets. Early surgery isrecommended to CSA patients who have failed conservative treatments. The zone de�nition establishedin current study may help the diagnosis of CSA for early surgical intervention.

To our knowledge, no study had examined the relative position of segmental ventral rootlet and pedicle.Here, we de�ned two zones in the coronal plane from cranial to caudal: pedicle zone (zone P) andinterpedicle zone (zone IP). At C3 pedicle level, the segmental spinal cord and ventral nerve rootlets of C4was at zone P. From C3 to C7, the position of segmental ventral rootlet and spinal cord become morerostral to the corresponding pedicle. For example, the segmental spinal cord and ventral nerve rootlets ofC8 was near to the inferior part of C6 pedicle. This �nding may help to explain why patients with disc

Page 7/12

herniation at C6/7 could have symptoms resulted from C8 nerve root compression. A previous studysuggested that C8 nerve root does not have contact with C7–T1 disc, and hence the chance of a direct C8nerve root compression by C7-T1 disc is very small [8]. However, current �ndings suggest that the chanceof compression of C8 ventral nerve rootlets by C6/7 disc is rather large. Furthermore, compressions ofzone I and zone II at C6/7 may also cause dysfunctions of C8 spinal cord and ventral nerve rootlets.While compression at zone III may lead to radiculopathy of both C7 and C8 ventral nerve rootlets.

Anatomical studies have been conducted to evaluate the width of the spinal segment [15-17]. Shinomiyaet al. [17] investigated the width of the spinal segment from C5 to C8 using cadavers and reported thatthe width at C6 was the widest, while that at C8 was the narrowest. Kobayashi et al. [18] also con�rmedthat C8 was the narrowest and this characteristic continued to the entry of the root in the foramen.Karatas et al. [16] measured the widths from C2 to C8, and found that the longest longitudinal length wasat the C5, while the shortest was at the C2. In current study, the longitudinal length of segmental ventralrootlets at C4 and C8 were shorter than those at C5, C6 and C7. 

As shown in Tanaka’s study [8], intradural intersegmental connections were rare in ventral rootlets (twoconnections out of 36 intersegments, 6%) and much thinner. Both connections were found between C4and C5 ventral rootlets. In this current study, we found three connections (two specimens) out of 20intersegments (15%) (Figure 5). One specimen had bilateral connections while the other had unilateralconnections. Both connections were found in C5/6 segment between ventral rootlets of C5 and C6 andwere relatively thinner compared with other bundles of the rootlets. This �nding may also help to explainwhy symptoms are sometimes diffuse with blurred nerve root location in patients with cervicalradiculopathy. There are some limitations of our study. The number of cadavers was small and thecadavers were formalin-�xed which may affect the accurate measurement.

ConclusionA comprehensive understanding of neurologic anatomy in cervical spinal canal is important to accuratediagnosis of cervical spondylosis. The cervical spinal canal was divided into different zones in this study.The current de�nition of anatomic zones may be useful for diagnosis of cervical spondylosis andconducting safe and effective anterior decompression surgery.  Further studies are needed to correlate theanatomic zones de�ned in current study with radiological �ndings and clinical symptoms in cervicalspondylosis patients.

List Of AbbreviationsLV: length of the cervical spinal cord segment at the ventral rootlets; PH: pedicle height; IPH: inter-pedicleheight; PN: distance between the superior margin of pedicle and the exit of the uppermost ventral nerverootlet; P: pedicle zone; IP: inter-pedicle zone; ANOVA: one-way analysis of variance; LSD: least signi�cantdifference; SD: standard deviation

Page 8/12

Declarations1) Ethics approval and consent to participate

This study was approved by the Ethical committee of Beijing Luhe Hospital. Each participant gavewritten, informed consent to participate.

2) Consent for publication

Consent for publish potentially-identifying information of patients was obtained.

3) Availability of data and materials

The datasets used and/or analyzed during the current study are stored in our hospital and are availablefrom the corresponding author on reasonable resquest.

4) Competing interests

The authors declare that they have no competing interests.

5) Funding

No funding was received.

6) Authors’ contributions

LYD did the measurement and wrote the paper. LL did the measurement and analyzed the data. KC didthe dissection and measurement. YX did the dissection. CXM designed the study and revised the paper.GY (Yan Gao) performed the statistical analysis. GY (Yun Guan) revised the paper. All authors have readand approved the manuscript.

7) Acknowledgements

We thank International Science Editing (http://www.internationalscienceediting.com) for editing thismanuscript.

References1. Kim HJ, Tetreault LA, Massicotte EM, et al. Differential diagnosis for cervical spondylotic

myelopathy: literature review. Spine (Phila Pa 1976). 2013;38:S78–S88.

2. Bono CM, Ghiselli G, Gilbert TJ, Kreiner DS, Reitman C, Summers JT, Baisden JL, Easa J, Fernand R,Lamer T, Matz PG, Mazanec DJ, Resnick DK, Shaffer WO, Sharma AK, Timmons RB, Toton JF; NorthAmerican Spine Society: An evidence-based clinical guideline for the diagnosis and treatment ofcervical radiculopathy from degenerative disorders. Spine J 11: 64–72, 2011.

Page 9/12

3. Shamji MF, Massicotte EM, Traynelis VC, Norvell DC, Hermsmeyer JT, Fehlings MG. Comparison ofanterior surgical options for the treatment of multilevel cervical spondylotic myelopathy: asystematic review. Spine (Phila Pa 1976). 2013;38:S195–S209.

4. Lebl DR, Bono CM. Update on the Diagnosis and Management of Cervical Spondylotic Myelopathy. JAm Acad Orthop Surg. 2015 Nov;23(11):648-60.

5. McCormack BM, Weinstein PR. Cervical spondylosis. An update. West J Med. 1996 Jul-Aug;165(1-2):43-51.

�. Hollinshead WH. Anatomy for surgeons. 3rd ed. Philadelphia: JB Lippin- cott, 1982;220–50.

7. MarzoJM,SimmonsEH,KallenF. Intraduralconnectionsbetweenadjacent cervical spinal roots. Spine1987;12:964–8.

�. Tanaka N, Fujimoto Y, An HS, Ikuta Y, Yasuda M. The anatomic relation among the nerve roots,intervertebral foramina, and intervertebral discs of the cervical spine. Spine (Phila Pa 1976). 2000Feb 1;25(3):286-91.

9. Veleanu C. Contributions to the anatomy of the cervical spine. Functional and pathogeneticsigni�cance of certain structures of the cervical vertebrae. Acta Anat (Basel). 1975;92(3):467-80.

10. Ebraheim NA, An HS, Xu R, Ahmad M, Yeasting RA. The quantitative anatomy of the cervical nerveroot groove and the intervertebral foramen. Spine 1996;21:1619 –23.

11. Yilmazlar S, Kocaeli H, Uz A, Tekdemir I. Clinical importance of ligamentous and osseous structuresin the cervical uncovertebral foraminal region. Clin Anat. 2003, 16(5):404-10.

12. Jiang SD, Jiang LS, Dai LY. Cervical spondylotic amyotrophy. Eur Spine J. 2011 Mar;20(3):351-7.

13. Zhang J, Cui C, Liu Z, Tong T, Niu R, Shen Y. Predisposing factors for poor outcome of surgery forcervical spondylotic amyotrophy: a multivariate analysis. Sci Rep. 2016 Dec 19;6:39512.

14. Jin X, Jiang JY, Lu FZ, Xia XL, Wang LX, Zheng CJ. Electrophysiological differences betweenHirayama disease, amyotrophic lateral sclerosis and cervical spondylotic amyotrophy. BMCMusculoskelet Disord. 2014 Oct 16;15:349.

15. Kubo Y, Waga S, Kojima T et al (1994) Microsurgical anatomy of the lower cervical spine and cord.Neurosurgery 34:895–900.

1�. Karatas A, Caglar S, Savas A, Elhan A, Erdogan A (2005) Microsurgical anatomy of the dorsalcervical rootlets and dorsal root entry zones. Acta Neurochir (Wien) 147:195–199.

17. Shinomiya K, Okawa A, Nakao K et al (1994) Morphology of C5 ventral nerve rootlets as part ofdissociated motor loss of deltoid muscle. Spine 19:2501–2504.

1�. Kobayashi R, Iizuka H, Nishinome M, Iizuka Y, Yorifuji H, Takagishi K. A cadaveric study of thecervical nerve roots and spinal segments. Eur Spine J. 2015 Dec;24(12):2828-31.

Figures

Page 10/12

Figure 1

An example image of a cadaveric specimen showing the spinal cord and ventral nerve rootlets from C4 toC8. VA: vertebral artery.

Page 11/12

Figure 2

Zone division of the cervical spinal canal. Zone I represents the area between bilateral origins of ventralnerve rootlet. Zone II contains the area between the origin of ventral nerve rootlets and lateral border ofspinal cord. Zone III represents the area between lateral border of spinal cord and medial margin of thepedicle. Zone P de�nes the area between the upper and lower margins of the corresponding pedicle. ZoneIP includes the area between the lower margin of the upper pedicle and the upper margin of the lowerpedicle. LV, length of the segmental ventral rootlets. PN, the distance between the superior margin ofpedicle and the exit of the uppermost ventral nerve rootlet.

Figure 3

Example of zone division at cervical segments. a, At C4/5 level, all C6 nerve rootlets were located at zoneIP, and zone III contains only C5 nerve rootlets. b, At C6/7 level of the same specimen, part of C8 nerve

Page 12/12

rootlets reaches zone P, zone III contains both C7 and C8 nerve rootlets.

Figure 4

a, The upper black circle shows the compression region in zone I, and the lower black circle shows thecompression in zone II. b, Intact cervical spinal cord without any compression.

Figure 5

a, Unilateral intradural intersegmental connection between C5 and C6. b, Bilateral intraduralintersegmental connections between C5 and C6.